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Effect of Epoxy Flux Underfill on Thermal Cycling Reliability of Sn-8Zn-3Bi Lead-Free Solder in a Sensor Application

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review


Original languageEnglish
Title of host publicationProceedings - ECTC 2016: 66th Electronic Components and Technology Conference
Number of pages7
ISBN (Electronic)9781509012039
Publication statusPublished - 16 Aug 2016
Publication typeA4 Article in a conference publication
EventIEEE Electronic Components and Technology Conference - , United States
Duration: 1 Jan 2000 → …


ConferenceIEEE Electronic Components and Technology Conference
CountryUnited States
Period1/01/00 → …


The use of sensors has significantly increased in both domestic and industrial applications. In some applications, the sensor component is used along with a heat-sensitive component, therefore, the attachment process using common lead-free solders that have high melting temperature (e.g., Sn-Ag-Cu, Tm = 217 °C) may be challenging. Among lead-free solders with low melting temperature, Sn-8%Zn-3%Bi (wt.%), lead-free solder has a rather similar melting temperature to that of typical Sn-Pb solders. In addition, it offers good mechanical properties. However, the presence of Zn makes it prone to oxidation especially at high temperatures. In this paper, the reliability of sensor attachments using Sn-8%Zn-3%Bi solder and epoxy flux underfill was studied under thermal cycling. Thermal cycling results showed that the lifetime of the lead-free solder joint was lower than that of the Sn-Pb-2Ag solder joints. Failure analysis revealed that the dominant failure mode in lead-free samples was delamination of the sensor pad. In contrast, the failure mode of Sn-36%Pb-2%Ag samples was fatigue crack inside the solder. Additionally, it was found that Sn-Zn-Bi lead-free solder was compatible with epoxy flux underfill.


  • Failure analysis, Sensor, Sn-Zn-Bi, Solder, Thermal cycling, Underfill

Publication forum classification

Field of science, Statistics Finland